Historic high tides from supermoon and sea level rise flood the Southeast coast

The scene in Charleston, S.C., on Tuesday morning during high tide. (Jessica Hofford)

Ocean water surged into neighborhoods on the Southeast coast on Tuesday morning during high tide, pushing gauges well beyond predicted levels. Seemingly overnight, spurred by sea level rise, we’ve entered an era where king tides compete with hurricanes in the water level record books.

Tuesday morning’s high tide peaked at 8.69 feet in Charleston, over a foot and a half higher than the predicted level. The highest crest on record in Charleston was 12.56 feet on Sept. 21, 1989 — the day that Hurricane Hugo made landfall in South Carolina.

The water level near Savannah, Ga., reached 10.43 feet, which was the third highest on record for the station. The top two records are 10.47 feet on Aug. 11, 1940, when a Category 2 hurricane made landfall on the Georgia and South Carolina coast, and 10.87 on Oct. 15, 1947, when Hurricane Nine made landfall in the same location.

Residents are saying Tuesday’s high tide was worse than South Carolina’s “1,000-year flood” in early October.

A combination of factors led to the inundation, including peak astronomical tide during a supermoon, onshore winds, a slowing Gulf Current and sea level rise.

According to a recent sea level rise report by the Union of Concerned Scientists, days with tidal flooding in Charleston have increased from two or three per year in the 1970s, to 10 or more now. NOAA reports that less destructive, “nuisance” flooding has increased by 400 percent in Charleston since the 1960s alone.

And the future is even wetter. Charleston is “also expected to face extensive flooding from tides alone by about 2030, because of sea level rise,” the UCS study says. “In places such as Charleston … less than half a foot of sea level rise will mean that high tides alone could flood substantial areas up to two dozen times per year.”

The same flavor of record-breaking coastal flooding has inundated parts of the Miami area over the past month, says Brian McNoldy, our tropical weather expert and Miami resident. “Since records began in 1996 at Virginia Key, the top four high-water events have all been associated with nearby hurricanes, and typically ones that coincided with the September and October king tides,” McNoldy wrote. “But on Sept. 27, the fifth highest water level was measured at the location, and there was no influence from a hurricane.”

Tides will continue to run higher than normal along the East Coast through Wednesday as the supermoon goes completely full, but the worst flooding is likely over for the South Carolina and Georgia coasts.

Angela FritzAngela Fritz is an atmospheric scientist and The Washington Post's deputy weather editor. Before joining The Post, Fritz worked as a meteorologist at CNN in Atlanta and Weather Underground in San Francisco. She has a BS in meteorology and an MS in earth and atmospheric science. Follow